It is well-known that the speed of an Otto or Diesel cycle engine output or crankshaft varies even during so-called steady-state operation of the engine, i.e., the shaft continuously accelerates and decelerates about the averages speed of the shaft. The accelerations and decelerations are, of course for the most part, a result of power pulses from the engine cylinders. The pulses may be of uniform frequency and amplitude when cylinder charge density, air/fuel ratio, and ignition are uniform. However, such uniformity does not always occur, thereby producing pulses which vary substantially in frequency and amplitude. Whether uniform or not, the pulses, which are herein referred to as torsionals, are transmitted through vehicle drivelines and to passengers in vehicles. The torsionals, which manifest themselves as vibrations, are detrimental to drivelines and derogate passenger-ride quality. Further, when an engine is abruptly accelerated and/or decelerated by accelerator pedal movement or other factors, torque pulses ring through the driveline and also derogate ride quality, such pulses are herein also referred to as torsionals.
Since the inception of automobiles, many torsional isolator mechanisms have been proposed and used to isolate and dampen driveline torsionals. The isolator mechanism proposed in U.S. Pat. No. 5,078,649 includes, as does the isolator mechanism herein, flat, long travel spiral springs connected in parallel with a vane damper device. Both mechanisms are disposed in a torque converter housing and immersed in the pressurized torque converter oil therein. U.S. Pat. No. 5,078,649 is incorporated herein by reference. The amount of damping (i.e., damping factor) provided by the vane damper device in this patent has been considered marginal in some applications due to valving arrangements employed therewith and leakage of oil from the working chambers of the damper. The isolator mechanism disclosed herein includes features for overcoming the above mentioned disadvantages.